A spark plug is mounted to an internal combustion engine and used to ignite a fuel gas in a combustion chamber of the internal combustion engine. There has been proposed a spark plug in which a magnetic member is disposed in a constant diameter axial hole of an insulator so as to suppress radio noise induced by fuel ignition. See, for example, Japanese Laid-Open Patent Publication No. S62-150681. In this spark plug, the magnetic member is formed in a cylindrical shape with a though hole; and an electrode member (more specifically, a terminal electrode) is inserted in the though hole of the magnetic member.
In the above-proposed spark plug, it is conceivable to increase the thickness of the magnetic member for the purpose of more effectively suppressing radio noise. However, the electrode member may be excessively narrowed with increase in the thickness of the magnetic member. There arises a problem that the excessively narrowed electrode member becomes bent and comes into contact with the magnetic member to thereby cause damage or breakage of the magnetic member. From the viewpoint of avoiding such a problem, it has conventionally been difficult or impossible to ensure the thickness of the magnetic member.
In view of the foregoing, an advantage of the present invention is a spark plug capable of ensuring the thickness of a magnetic member without excessively narrowing an electrode member.